From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46066][MODERATE REGULAR] ceph: fix num_ops off-by-one when crypto allocation fails Date: Wed, 27 May 2026 11:16:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46066 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 6200f41d6fcf2ac7e24866431e381cbc914560e4 List-Id: CVE: CVE-2026-46066 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ceph: fix num_ops off-by-one when crypto allocation fails Commit: 6200f41d6fcf2ac7e24866431e381cbc914560e4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6200f41d6fcf2ac7e24866431e381cbc914560e4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46066 Analysis date: Wed, 27 May 2026 11:16:53 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A local user writing sparse data to fscrypt-enabled CephFS files under memory pressure can trigger a writeback `num_ops` accounting mismatch and kernel panic, with no demonstrated memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46066 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46066 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: MODERATE REGULAR Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-46066 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';CWE-193;CWE-617;CWE-755;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A local denial of service can occur in CephFS encrypted writeback when bounce buffer allocation fails after ceph_wbc num_ops has already been incremented for a new discontiguous extent. The failed folio is redirtied and not added to the batch, but the stale num_ops value can later make ceph_submit_write() hit BUG_ON and panic the kernel. For the CVSS the PR:L is used because a local user with write access to an fscrypt enabled CephFS file can trigger the writeback pattern, although reliable reproduction also requires memory pressure and a sparse 4KiB write pattern. The issue is not directly network reachable and does not involve UAF, out of bounds write, arbitrary write, information disclosure, or privilege escalation. Impact is primarily denial of service via kernel panic, with only weak integrity concern from writeback accounting mismatch.';NO MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) YES WRITE OOB DANGER DISK KERNEL_PANIC_PLUS_UAF LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 A local user with write access to an fscrypt-enabled CephFS file can create the sparse write pattern involved in the bug. * Reliable kernel crash / strong DoS: +1 The described failure reaches `BUG_ON(ceph_wbc->op_idx + 1 != req->r_num_ops)`, causing a kernel panic. * Availability impact realistic: +1 Successful triggering can crash the kernel. * Important filesystem/storage path: +1 This is in CephFS encrypted writeback and write extent accounting. Subtracting signals: * Hard/special condition: -1 Reliable reproduction requires encrypted CephFS, a 4KiB written / 4KiB skipped pattern, and memory pressure sufficient to make bounce buffer allocation fail. * Configuration-dependent exposure: -1 Requires CephFS with fscrypt-enabled files and affected kernel versions where multi-folio encrypted writeback is active. Paranoid additional signal: * Weak integrity concern: +1 The root cause is writeback extent accounting mismatch. The demonstrated result is panic, not data corruption, but filesystem writeback accounting bugs deserve limited manual scrutiny. No signals apply for UAF, OOB write, arbitrary write, page-cache corruption, information disclosure, remote reachability, or privilege escalation. ## 3. Reachability analysis The trigger is local writeback activity against fscrypt-enabled CephFS files. A user who can write to such files can shape the sparse write pattern, but reliable triggering also needs memory pressure to make the encryption bounce buffer allocation fail. Namespaces and containers matter only if they can write to the affected CephFS mount and induce memory pressure. The issue is not directly network reachable, although CephFS itself is a network filesystem. ## 4. Severity interpretation This behaves primarily as a local filesystem DoS. The patch fixes an off-by-one accounting error in `ceph_wbc->num_ops` after a failed encrypted writeback folio move. Theoretical integrity concern is limited because the bug is in writeback accounting, but the commit specifically shows a `BUG_ON` panic before successful submission with mismatched ops. There is no evidence of memory corruption, data disclosure, or privilege escalation. ## 5. One-sentence report phrase A local user writing sparse data to fscrypt-enabled CephFS files under memory pressure can trigger a writeback `num_ops` accounting mismatch and kernel panic, with no demonstrated memory corruption or privilege escalation. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is DoS-only based on the patch, but it affects encrypted CephFS writeback accounting and can be triggered by local file writes under specific conditions, so limited manual validation of deployment exposure is useful. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ceph: fix num_ops off-by-one when crypto allocation fails Commit: 6200f41d6fcf2ac7e24866431e381cbc914560e4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6200f41d6fcf2ac7e24866431e381cbc914560e4 Commit description: move_dirty_folio_in_page_array() may fail if the file is encrypted, the dirty folio is not the first in the batch, and it fails to allocate a bounce buffer to hold the ciphertext. When that happens, ceph_process_folio_batch() simply redirties the folio and flushes the current batch -- it can retry that folio in a future batch. However, if this failed folio is not contiguous with the last folio that did make it into the batch, then ceph_process_folio_batch() has already incremented `ceph_wbc->num_ops`; because it doesn't follow through and add the discontiguous folio to the array, ceph_submit_write() -- which expects that `ceph_wbc->num_ops` accurately reflects the number of contiguous ranges (and therefore the required number of "write extent" ops) in the writeback -- will panic the kernel: BUG_ON(ceph_wbc->op_idx + 1 != req->r_num_ops); This issue can be reproduced on affected kernels by writing to fscrypt-enabled CephFS file(s) with a 4KiB-written/4KiB-skipped/repeat pattern (total filesize should not matter) and gradually increasing the system's memory pressure until a bounce buffer allocation fails. Fix this crash by decrementing `ceph_wbc->num_ops` back to the correct value when move_dirty_folio_in_page_array() fails, but the folio already started counting a new (i.e. still-empty) extent. The defect corrected by this patch has existed since 2022 (see first `Fixes:`), but another bug blocked multi-folio encrypted writeback until recently (see second `Fixes:`). The second commit made it into 6.18.16, 6.19.6, and 7.0-rc1, unmasking the panic in those versions. This patch therefore fixes a regression (panic) introduced by cac190c . Cc: stable@vger.kernel.org Fixes: d552077 ("ceph: add encryption support to writepage and writepages") Fixes: cac190c ("ceph: fix write storm on fscrypted files") Signed-off-by: Sam Edwards Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Sasha Levin Changed files: fs/ceph/addr.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6200f41d6fcf2ac7e24866431e381cbc914560e4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46066 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46066 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H The Best / paranoid CVSS score: 5.3 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: 2 Paranoid ActionableScore: 3 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE REGULAR These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).